insane - expecting others to be like one self

in round about ways, very cleverly, how do some people, take it upon themselves to imply that others feel like they themselves do?

why is this method used in personal dealings with other people, even those who ought to be honestly treated?

is it learnt cultural smartness?
is it a way to feel personally justified in feeling and creating an illusion of a feeling in oneself, by projecting it onto others?

any thoughts?